Revisiting growth hormone nadir cut-offs for remission in patients with acromegaly

Objective: Over the past decade, the growth hormone (GH) nadir cut-off during the oral glucose tolerance test for remission in patients with acromegaly was changed from 0.4 to 1.0 μg/L due to the limited use of ultrasensitive detection kits to measure GH levels. However, the optimal cut-off level for GH nadir remains unclear. This retrospective study aimed to investigate the association between different GH nadir cut-offs and prognosis in patients with acromegaly. Design and methods: A total of 285 patients with acromegaly with a glucose-suppressed GH nadir <1 μg/L at 3–6 months after trans-sphenoidal adenomectomy were divided into two groups according to the glucose-suppressed GH nadir levels at 3–6 months post-operatively (group A: <0.4 μg/L; group B: 0.4–1.0 μg/L). GH levels were measured using an ultrasensitive IRMA. The clinical, hormonal, metabolic, and neuroradiological data of the two groups were compared. Results: Female sex, as well as confirmed macroadenomas, was significantly overrepresented in group B. The 5-year rate of patients who achieved nadir GH < 1.0 μg/L and age- and sex-matched normal IGF-1 was significantly higher in group A than that in group B. However, there was no significant difference between the two groups in metabolic parameters at 12 months post-operatively. Conclusion: Different GH nadir cut-offs were associated with different 5-year rates of patients who achieved nadir GH <1.0 μg/L and age- and sex-matched normal IGF-1, suggesting that a strict GH nadir threshold of 0.4 μg/L correlates better with remission.